The paper is a comprehensive survey into the state-of-the-art in geothermal reservoir engineering, and while there is a general lack of hard quantitative data, there is rapid progress beginning to be made in the field. The presentation takes the form of a survey paper, examining the nature of geothermal reservoirs, the hardware and software associated with geothermal reservoir engineering, the research plans and accomplishments of the geothermal reservoir engineering subtask within the Hawaii Geothermal Project, and an international survey on the subject. Sections are provided to enable quick orientation to the field of geothermal reservoir engineering.